The present invention relates to a device for injection-molding a part, in particular a wax model.
Such a model is used in a lost wax molding method in a number of fields and for example for molding high pressure turbine blades for a turbine engine such as a turboprop or a turbojet.
In this method, one or more parts are injection-molded by using injection-molding tooling that has a cavity of shape corresponding to the shape of the model that is to be obtained. When the model has a cooling circuit, a ceramic core is used. In this event, the wax is injected into the cavity, around the core.
The wax models as obtained in this way are then mounted as a cluster on a support.
The cluster is then dipped in a bath of ceramic, referred to as a slip, and then dusted with a ceramic powder (stuccoworking). Dipping and stuccoworking are repeated several times until a layer of ceramic is obtained that is sufficiently thick and that forms a shell around the cluster.
The wax is then removed from the ceramic shell by passing the assembly in an autoclave where steam under pressure and at high temperature causes the wax to melt (dewaxing).
The shell is then baked in an oven in order to acquire sufficient mechanical strength for it to be used as a mold.
Metal, e.g. a nickel-based alloy, is then cast into the shell. After cooling, the shell is knocked out and then the various parts are removed from the cluster, i.e. they are separated from their common support.
When a core is used, it is removed chemically with the help of a bath.
The parts are then trimmed, ground, and then inspected.
As a general rule, tooling for injection-molding the wax model comprises two cavity blocks having a cavity formed therein of shape that matches the shape of the part that is to be molded once the cavity blocks are superposed. At least one of the cavity blocks is fitted with means for positioning the core, which means comprise at least one bearing surface for bearing against the core and at least one presser screw screwed into a threaded passage of the cavity block for the purpose of holding the core in position.
The core must be clamped strongly enough for it to be held properly in position and to ensure that it does not move while parts are being molded. However, if this clamping is too strong, that can deform, move, or damage the cores, such that the final parts made by molding no longer comply with their specifications.
A particular object of the invention is to provide a solution to this problem that is simple, effective, and inexpensive.